# Java14安装
## 1.jdk最新版本
截止目前,jdk版本已经更新到14
## 2.jdk14新特性
`https://openjdk.java.net/projects/jdk/14/` --openjdk网站我们可以看到有以下16大特性
```http request
305: Pattern Matching for instanceof (Preview)
343: Packaging Tool (Incubator)
345: NUMA-Aware Memory Allocation for G1
349: JFR Event Streaming
352: Non-Volatile Mapped Byte Buffers
358: Helpful NullPointerExceptions
359: Records (Preview)
361: Switch Expressions (Standard)
362: Deprecate the Solaris and SPARC Ports
363: Remove the Concurrent Mark Sweep (CMS) Garbage Collector
364: ZGC on macOS
365: ZGC on Windows
366: Deprecate the ParallelScavenge + SerialOld GC Combination
367: Remove the Pack200 Tools and API
368: Text Blocks (Second Preview)
370: Foreign-Memory Access API (Incubator)
```
下面我们就常用到的特性改变举例看一下
1.305: Pattern Matching for instanceof (Preview) instanceof新特性
```java
//以前我们是这么使用的
if (obj instanceof String) {
String s = (String) obj;
// use s
}
//新特性我们可以这么使用,即将强制转换类型绑定给变量,但变量只能在true块中使用
if (obj instanceof String s) {
// can use s here
} else {
// can't use s here
}
if (!(obj instanceof String s)) {
// can't use s here
} else {
// can use s here
}
//可以在&&后使用, 但不能在||后使用
if (obj instanceof String s && s.length > 10) {
// can use s here
}
```
2.359: Records (Preview) 记录类型
```java
import static java.util.Calendar.*;
//有望替代lombok
public class Test {
public record User(int x, int y) {
}
public static void main(String[] args) {
User user = new User(1, 2);
System.out.println(user.x);
System.out.println(user.y);
}
}
```
3.361: Switch Expressions (Standard) switch语法形式改变
```java
import static java.util.Calendar.*;
public class Test {
public static void main(String[] args) {
formatWeek(0);
formatWeek(1);
formatWeek(2);
formatWeek(3);
formatWeek(4);
formatWeek(5);
formatWeek(6);
System.out.println(formatWeek2(5));
System.out.println(formatWeek2(6));
}
public static void formatWeek(int day) {
switch (day) {
case MONDAY -> System.out.println("MONDAY");
case TUESDAY -> System.out.println("TUESDAY");
case WEDNESDAY -> System.out.println("WEDNESDAY");
case THURSDAY -> System.out.println("THURSDAY");
case FRIDAY -> System.out.println("FRIDAY");
case SATURDAY -> System.out.println("SATURDAY");
case SUNDAY -> System.out.println("SUNDAY");
}
}
public static String formatWeek2(int day) {
String str = switch (day) {
case MONDAY -> "MONDAY";
case TUESDAY -> "TUESDAY";
case WEDNESDAY -> "WEDNESDAY";
case THURSDAY -> "THURSDAY";
case FRIDAY -> "FRIDAY";
case SATURDAY -> "SATURDAY";
case SUNDAY -> "SUNDAY";
default -> "NONE";
};
return str;
}
}
```
4.368: Text Blocks (Second Preview) 文本块
```java
//old
String html = "
" +
"
" +
" Hello, world
" +
"
" +
"
";
//new
String html = """
Hello, world
""";
```
## 3.jdk14的安装
### 3.1macOS安装
下载最新的jdk-14.0.1_osx-x64_bin.dmg包, `https://www.oracle.com/java/technologies/javase-jdk14-downloads.html`
按步骤安装即可,自动配置环境变量,安装完`java -version` 查看显示版本号即安装成功
### 3.2linux安装
下载最新的jdk-14.0.1_linux-x64_bin.tar.gz包
#### 3.2.1解压包
```shell script
cd /usr
mkdir java
cd java
#将.tar.gz包拷贝到java目录
tar zxvf jdk-14.0.1_linux-x64_bin.tar.gz
```
#### 3.2.2配置环境变量
在/etc/profile配置文件里追加以下配置即可
```shell script
export JAVA_HOME=/usr/java/jdk-14.0.1
export PATH=$JAVA_HOME/bin:$PATH
```
`java -version` 查看显示版本号即安装成功